242 Van Name and Edgar — Velocities of Certain Reactions 



until the volume had been reduced to 380 cc , which was thought 

 to be a safe limit. Under these conditions the mercury goes 

 into solution as the complex ion Hgl/', and no mercurous salt 

 appears to be formed. The samples were carefully titrated 

 with JST/20 sodium thiosulphate, using starch as indicator. 

 The burette used had been certified by the Berlin Reichsanstalt. 



In Table I are given the results of the experiments with 

 mercury and iodine. The four columns taken in order contain : 

 1st, the' concentration c, of the iodine in gram atoms per liter* : 

 2d, the time interval At (the same as t^ — tj), in minutes; 3d, 

 the volume v, in cubic centimeters ; 4th, the velocity constant, 

 K, as calculated by the equation above. The speed of stirring, 

 in revolutions per minute, is denoted by r. In this and the 

 following tables abnormal values of the constant, indicated by 

 parentheses, have been disregarded in calculating the averages. 

 It may be stated in this connection that the experiments recorded 

 in this article include all that were made with the exception of 

 preliminary experiments and a few affected by known errors. 



On comparing the experiments carried out with like rates of 

 stirring it is evident that the velocity of the reaction is greater 

 the higher the concentration of the potassium iodide. This 

 effect of the iodide will be equally conspicuous in the experi- 

 ments with other metals, and will be discussed later. An 

 increase in the rate of stirring also accelerates the reaction, as 

 was to have been expected, the value of the constant being 

 here approximately proportional to the 4-/5 power of r. 



To obtain the temperature coefficient of the reaction a 

 single experiment was carried out at 35° with the following 

 result : 



Exp. 9. — Mercury and Iodine at 35°. 

 K = (1C 



00 g. KI per liter. 



r — 240 





3), 11-68 11-35 



11-50 11-53 



11-59 





Average 



11-53 



The ratio of this constant to that of experiment 2 gives 1-3 

 as the temperature coefficient for 10°. This is in sharp con- 

 trast with the usual value of — {t 10 ° for reactions in homoge- 



I*-t 

 neous systems, which is on the average about twice as large. 



In the experiments with metals other than mercury the 

 method followed only differed from that just described in that 

 the metal disk, after its insertion into the solution, was allowed 

 to remain in position until the close of the experiment, and the 

 calculations were based upon the time intervals between suc- 



* Halogen concentrations are expressed in these units throughout this 

 article. 



